Bone graft materials derived from mineralized gelatin

ABSTRACT

The present invention provides novel methods of forming mineralized gelatin carriers from bone. The present invention further provides mineralized gelatin carriers themselves; bone products that include such mineralized gelatin carriers including DBM bone products; and kits that include mineralized gelatin carriers formed from bone. The present invention further provides methods for making DBM bone products, wherein both the DBM and a mineralized gelatin carrier for the DBM are derived independently from a bone lot.

CLAIM FOR PRIORITY

This application is a continuation of U.S. application Ser. No.11/362,540 filed on Feb. 27, 2006, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention provides novel methods of forming mineralizedgelatin carriers from bone, such as cortical or cancellous bone. Thepresent invention also provides mineralized gelatin carriers themselves;bone products that include such mineralized gelatin carriers includingDBM bone products; and kits that include mineralized gelatin carriersformed from bone. The present invention further provides methods formaking bone products, wherein both the bone graft products and amineralized gelatin carrier are derived independently from a bone lot.Also provided are surgical implants and devices that include mineralizedcarriers or bone products thereon or incorporated therewith. The presentinvention further provides methods of treatment using mineralizedcarriers, bone products, or surgical implants or devices of the presentinvention.

BACKGROUND OF THE INVENTION

Bone grafting is a common procedure performed by orthopedic trauma andspinal surgeons to regenerate tissue at a site affected by trauma,disease, or deformity. Graft materials include bone taken from thepatient's own skeleton, allograft bone derived from tissue donors, andsynthetics that consist of porous ceramics and polymers. Demineralizedbone matrix (DBM), is a special type of bone graft that activelystimulates bone formation due to the presence of growth factors withinthe DBM particles, Derived from allogeneic cortical bone, DBM has beenwidely used in a variety of orthopedic cases. However, the particulatenature of DBM has made its delivery and containment difficult.

To improve the handling properties of DBM, several companies havedeveloped products that combine DBM particles with a gel-like carrier totry to improve the handling and graft containment of DBM at the surgicalsite. However, not all carriers perform equally well as a DBM deliveryvehicle. For example, the combination of glycerol and DBM, disclosed inU.S. Pat. No. 5,073,373, results in a moldable putty, however, theglycerol component is highly soluble in water and body fluids, and canreadily wash away from the graft site. The combination of a thermallyreversible copolymer and DBM, disclosed in U.S. Pat. No. 6,309,659,improves upon the solubility of the carrier, however, studies have shownthat the final product has variable biological activity [Wang J C, etal. “Prospective comparison of commercially available demineralized bonematrix for spinal fusion”. Trans. North Am. Spine Soc 2000; 15:35-37].Another DBM product, disclosed in U.S. Pat. No. 6,652,887, is acombination of calcium sulfate, carboxymethylcellulose, water, and DBM.Although this product handles well and is resistant to irrigation, theDBM is enclosed in a carrier that disadvantageously takes 6 to 8 weeksto resorb. With typical graft incorporation occurring within the first72 hours, the delayed resorption of the carrier can interfere with thehealing response. [Lee Y P, Wang J C, Kanim L E, Jo M J, Davis M,Lieberman J R. “The direct comparison of different commerciallyavailable demineralized bone matrix substances in an athymic rat model.”Trans North Am Spine Soc 2001; 16:86-87].

The use of bone in gelatin manufacturing has been a widely used processsince the early 1900s. By weight, bone is approximately 70% mineral, 20%collagen, 5% growth factors, and 5% water [Bostrom, M P, Boskey A,Kaufman J K, Einhorn T A. “Form and Function of Bone.”Orthopaedic BasicScience. Buckwalter J A, Einhorn T A, Simon S R. (eds). Rosemont:American Academy of Orthopaedic Surgeons. pp. 327-328 (2000)]. Throughvarious processing methods, the cross-linked collagen component of bonecan be broken down to create gelatin. The gelatin molecule consists ofcollagen fragments that interact together to form rigid and semi rigidgels at room temperature and below. Standard gelatin manufacturingprocesses using bone as a raw material, start by treating the bone withan acidic solution to dissolve the bone mineral. The remaining materialcalled ossein is composed of 80% collagen by dry weight. A combinationof acids, bases, and high temperature can be used to break apart thecollagen molecules in ossein to create gelatin fragments. Done inseveral extraction steps, a range of purified gelatin solutions can beobtained. Similar processing has been disclosed to create gelatin fromhuman bone to be used as a carrier for DBM. All of these techniques useDBM as a starting material. Although DBM and ossein are chemicallysimilar, DBM processing is slightly different in that care must be takento maintain biological activity of the growth factors found in bone.

In commercial gelatin production, more aggressive processes are usedduring demineralization because the goal is to eventually extract onlypurified gelatin. Gendler et al. followed standard gelatin processingand discloses a method for treating DBM with high temperatures andpressures to thermally degrade the collagen to create gelatin (U.S. Pat.No. 6,576,249). This was accomplished using autoclaves and otherpressure vessels. Although the biological activity of the DBM isdestroyed, active DBM is added back to the gelatin to create a DBMputty. Although human gelatin is formed using the Gendler process, thesingle step exposure of DBM to pressure and temperature produces gels oflow quality with varying properties. The resulting DBM bone graftputties have poor handling and vary from lot to lot.

Kay et al. used a gentler approach to extracting gelatin by treating DBMwith acids, bases, and/or salts to chemically degrade the collagen atroom temperature and below (US Published Patent Application2003/0044445). In this process, the room temperature extraction canmaintain some of the biological activity of the growth factor content ofDBM. However, the low temperature extraction limits the amount andquality of gelatin produced from the extraction process. In bothtechniques, DBM is used as a starting material, and the resulting gel iscomposed of protein fragments from collagen and other proteins found inhuman DBM. Bone graft materials manufactured from these gels are formedby combining the DBM-derived gelatin with DBM particles.

SUMMARY OF THE INVENTION

The present invention provides novel techniques for creating amineralized gelatin carrier from bone. In the present processes, bone(such as cortical bone or cancellous bone), not DBM, is used as thestarting material. The use of mineralized bone allows for the resultantgelatin to contain the calcium and phosphate ions used during the boneregeneration process. Additionally, the process is conducted in a seriesof extraction steps which allow for the isolation of high quality humangelatin. Using a combination of acid, heat, and ultrasonic agitation,bone can be solubilized into a gelatin solution that contains bonemineral. These processes not only chemically and thermally degrade thecollagen into gelatin fragments, but also dissolve the calcium phosphatebone mineral. Various processes may optionally be used to solubilize thebone into a gelatin solution containing bone mineral. For example,various combinations of heat, acids, sonication, bases, salts, and/orpressure may be used. Once neutralized, the gelatin solution containsboth collagen fragments and soluble salts of calcium and phosphate.After the gelatin solution is cooled, this results in a mineralized gelthat makes an effective carrier for particulate DBM. In addition toeffectively delivering and maintaining the DBM graft at the surgicalsite, the mineralized gel also provides the bone regeneration site witha source of calcium and phosphate ions needed during remineralization.

In particular, the present invention provides methods of formingmineralized carriers from bone, and is further directed to mineralizedcarriers produced from such methods. The present invention furtherprovides mineralized carriers that include calcium and phosphate,regardless of their method of production. By way of non-limitingexample, the calcium and phosphate may be in the form of salts ofcalcium and phosphate.

The present invention also provides methods for producing bone products,which include one or more bone graft materials and one or moremineralized carriers. The bone graft materials include, but are notlimited to, demineralized bone matrix (DBM), autograft bone, allograftcortical bone, allograft cancellous bone, synthetic bone grafts such ascalcium phosphate and polymer bone graft substitutes, cellular materialssuch as marrow cells, osteoblasts, or mesenchymal stem cells, and/orgrowth factors such as BMP, TGF-B, VEGF, and FGF. The bone graftmaterial and the mineralized carriers used to make such products mayeach be independently formed from bone, such as cortical bone. Thepresent invention further provides bone products that include one ormore bone graft materials and one or more mineralized carriers. Boneproducts in accordance with the present invention may be in the form ofsheets, putties, pastes, sponges, gels, blocks and the like, and may beformed into any desired shape.

The present invention further provides kits, which include one or moremineralized carriers. The mineralized carriers included in such kits maybe formed from bone in accordance with the methods of the presentinvention. Alternatively, the one or more carriers may be formed usingother methods, which result in a mineralized carrier that includescalcium and phosphate, for example in the form of salts.

Kits in accordance with the present invention may further include one ormore additional components, for example, a liquid for reconstitutingmineralized carrier from a powder or other dried form; a container forcombining the carrier with one or more other components; an apparatus(such as a form or mold) in which or on which to form a mineralizedcarrier into a specific shape; and/or DBM or other bone graft componentsto be combined with the carrier, for example such that the user candetermine the ratio of DBM to carrier they wish to use.

The present invention also provides surgical implants or devicesincluding mineralized carriers or bone graft products incorporatedtherewith or thereon. Further provided are methods of treatment, whichinclude injecting or inserting a bone graft product, surgical implant ordevice in accordance with the present invention, into a patient in needthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a general process for creating a mineralizedDBM putty from a single lot of cortical bone, in accordance with certainembodiments of the present invention.

FIG. 2 is a flow chart of a detailed process for creating a mineralizedgelatin carrier, in accordance with certain embodiments of the presentinvention. Mineralized carriers of the present invention may be used tocarry DBM and/or other products such as autograft bone chips, allograftcortical bone chips, allograft cancellous bone chips, synthetic bonegrafts, growth factors (BMP, TGF, VEGF, etc), cells (stem cells, marrowcell, osteoblasts), or any other material used in bone grafting.

FIG. 3 is a photograph of a gel of both standard and mineralizedgelatin.

DETAILED DESCRIPTION OF THE INVENTION

The aspects, advantages and other features of the invention will becomeapparent in view of the following detailed description, which disclosesvarious non-limiting embodiments of the invention. In describingembodiments of the present invention, specific terminology is employedfor the sake of clarity. However, the invention is not intended to belimited to this specific terminology. It is to be understood that eachspecific element includes all technical equivalents that operate in asimilar manner to accomplish a similar purpose. Additionally, all of thecitations herein are incorporated by reference in their entirety.

As used herein, “a” or “an” may mean one or more. As used herein,“another” may mean at least a second or more.

As used herein, the terms “gel” and “gelatin” are used as they areunderstood in the art, and are used somewhat interchangeably herein. Theterm “gel” generally refers to a semi-solid form of “gelatin,” which isa derived protein formed from the collagen of animal tissues. The term“gelatin solution” refers to a liquid or semi-liquid that includesgelatin. However, the use of the terms gel and gelatin are not intendedto exclude liquid forms, which may convert to a non-liquid form, forexample upon cooling.

The terms “mineralized gelatin,” “mineralized gelatin carrier,”“carrier” and “mineralized carrier composition” are all intended toencompass a composition that includes a mineralized carrier inaccordance with the present invention, whether it is a carrier formed bythe present methods (or variant methods that are intended to beencompassed by the present methods), or a carrier that has similarmineral properties as the mineralized carrier formed by the presentmethods. As discussed further herein, such carriers or compositions, andbone products that include such carriers or compositions include, butare not limited to a mineralized carrier, and optionally one or moreadditional ingredients.

In developing a suitable carrier for a bone graft material, the carriermay advantageously be a biocompatible gel that can effectively deliverand maintain the material, such as DBM, at the graft site of a patient.The carrier should be readily absorbed by the site within the first fewweeks and should not interfere with the biological activity of thematerial, such as the growth factor component of DBM. Additionally, thecarrier may contain materials that can aid in the regeneration of bone.

The present invention includes methods for deriving a mineralizedgelatin carrier from human bone and for creating bone grafts. Prior gelscreated from processes that use demineralized bone as the startingmaterial for the carrier are missing the natural mineral component foundin typical bone grafts such as autograft and allograft. Using corticalor cancellous bone in the present processes gives the present gelatin amineral component. From a grafting standpoint, the local cells thatcreate new tissue must remineralize to form mature bone. Therefore, itis advantageous to provide a source of bone mineral to the site to aidthis remineralization process. Additionally, the present processes areadvantageous over processes that do not use heat, because heat of thepresent processes aids in the solubilization of the gelatin. Therefore,the present processes result in better quality gelatins. Furthermore,the present process for creating gelatin can use two or more extractionsteps which prevent continued degradation of the gelatin solution duringextraction. By limiting exposure of the gelatin solution to heat andacidic conditions in certain embodiments, the degradation process can becontrolled and better quality gelatins can be extracted. This in turngives products of the present methods a more cohesive feel and bettergraft containment properties.

Accordingly, the present invention provides methods for making a DBMbone product, which include separating a bone lot into a first portionand a second portion; processing the first portion to create drieddemineralized bone matrix; extracting a mineralized gelatin solutionfrom the second portion; neutralizing the extracted mineralized gelatinsolution; converting the mineralized gelatin solution to a freeze driedmineralized gelatin; combining the freeze dried gelatin with water toform a gelatin solution with a specific concentration, and combining thedried demineralized bone matrix with the mineralized gelatin to form aDBM bone product. The extraction process may include for example, one ormore steps of exposing the second portion of the bone lot to one or moreof elevated temperatures, acids, sonication, bases, salts, and/orpressure. Additionally, the step of converting the mineralized gelatinsolution to a mineralized gelatin may include refrigeration tofacilitate the formation of a solid gel. According to certainembodiments, the DBM may be combined with the mineralized gelatin whilethe mineralized gelatin is in a solution or powder form.

Methods of the present invention may further include-freeze-drying theDBM bone product. According to these embodiments, methods may furtherinclude re-hydrating the freeze-dried bone matrix product.

According to certain embodiments of methods for making a DBM boneproduct in accordance with the present invention, a DBM product may becreated as depicted in FIG. 1. According to these embodiments, a singlelot of donor bone is processed as depicted in the flow chart of FIG. 1.In particular, FIG. 1 depicts the splitting of a lot of freeze dried,ground cortical bone (2) for use in making DBM on the left of FIG. 1,and for use in preparing a mineralized gelatin carrier on the right ofFIG. 1, which may be combined in accordance with the present inventionin numerous different ways to form various DBM or bone graftingproducts.

The cortical bone lot (2) can be split by weight in a ratio depending onthe gelatin yield. For example, the ratio of DBM bone to carrier bonecan range from about 40:60 to about 95:5 by weight (i.e., the ratio ofthe weight of cortical bone used to produce DBM on the left of FIG. 1 tothe weight of cortical bone used to produce a gelatin carrier on theright of FIG. 1). The ratio is a ratio of the original bone lot.According to certain embodiments, the split may be about 80:20 to about95:5 or about 90:10. The actual ratio is dependent on the yield ofgelatin from the mineralized gelatin process.

Using an example ratio of 90:10, 90% of the cortical bone lot (i.e., thefirst portion of the bone lot, which is being used to produce DBM) maybe processed in a demineralization process (4) using standarddemineralization techniques. For example, in step (4) ground corticalbone may be soaked in an acidic solution, such as 0.5 N hydrochloricacid (HCl) solution for a period of about 2-5 hours. This may be donefor example, at around room temperature. By way of further example, inthe demineralization process, the acid extraction may be done at atemperature that does not denature the collagen. This mineralizedextract is then discarded, hence the term “demineralization”. After themineral is dissolved from the cortical bone, demineralized bone matrixparticles remain. The DBM may then undergo a neutralization step (6) inwhich the DBM may be rinsed with water and/or saline and neutralized bybuffering to bring the pH to 7. The wet DBM may then be subjected to afreeze-drying step (8) in which the wet DBM is freeze-dried into a dry,particulate form.

During the processing of the bone to form dried DBM, care should betaken to ensure that the biologically active growth factors maintaintheir activity. This may be done by minimizing the exposure of the boneand resultant DBM to high temperatures. It should be noted that thetechniques depicted on the left of FIG. 1 may include anydemineralization techniques known to those skilled in the art and arenot limited to the specific technique set forth in FIG. 1 or totechniques discussed in this application.

The remaining 10% of the cortical bone lot (i.e., the second portion ofthe cortical bone lot, which is being used to produce a carrier, such asgelatin) may be processed to create the mineralized gelatin. In thisprocess, gelatin is removed from the bone in an extraction process (10).The extraction process (10) may include exposing the second portion ofthe cortical bone lot to one or more of heat, acids, sonication, bases,salt, and/or pressure. For example, the bone may be placed in a moreconcentrated solution of acid than what is used in the processing ofDBM, such as HCl, and heated to near boiling to dissolve the bonemineral and fully denature the collagen molecules into gelatin. Inaddition, sonication may be used to ultrasonically agitate the particlesto accelerate the gelatin extraction process. In the gelatin extractionprocess, mineral is dissolved, but the higher temperature also denaturesthe collagen. In addition, in embodiments in which acid is used in theextraction process, an acid extraction solution (containing the mineral)is not removed and discarded. It becomes part of the gel.

The extraction process may include more than one extraction step. Thisproduces a high quality mineralized gelatin solution, which may then beneutralized according to neutralizing step (12) and converted to amineralized gelatin. According to the embodiments depicted in FIG. 1,the neutralized gelatin solution may undergo a freeze-drying step (14).The freeze-dried gelatin may be subjected to a reconstituting step (16)in which the gelatin is reconstituted with water or other solvent toform a gelatin solution with a specific concentration. Typically, thereconstituted gelatin solution is in the range of about 1-10% gelatinsolution.

According to the embodiments depicted in FIG. 1, the mineralized gelatinsolution may be subjected to a refrigeration step (18) in which thesolution (either directly after neutralization step 12 or after thereconstituting step 16) is cooled to form a solid gel.

Specific techniques to accomplish the extraction, neutralization and/orconversion to mineralized gelatin may include, but are not limited to,methods in accordance with the present invention for making amineralized carrier from cortical bone, discussed below. Variant methodsmay be employed however and remain within the scope of the presentinvention. For example, such methods may include forming a mineralizedcarrier from bone (rather than from DBM), and/or forming a mineralizedcarrier that includes calcium and phosphate. Additionally, the presentinvention includes forming a mineralized gelatin carrier by addingcalcium and phosphate materials to a standard gelatin.

DBM and/or other bone graft materials can then be combined (20) with thegel to create a variety of bone graft products. Products resulting fromthe combination of the gel and the DBM in the examples depicted in FIG.1 can be for example, in the form of a moldable putty, an extrudablegel, or a freeze dried sheet or block form, or any form in which the useof DBM may be advantageously used. By way of non-limiting example, thecombination of DBM and gelatin may be processed in step 22 to form DBMputty.

The present invention is further directed to methods of forming amineralized carrier from bone. The processing of bone may includeextraction for example by exposure to one or more of heat, acids,sonication bases, salts, and/or pressure, to form an extracted gelatinsolution; and neutralizing the extracted gelatin solution to form aneutralized solution. The processing may further include freeze-dryingthe neutralized solution to form a freeze-dried mineralized carrier.These steps are non-limiting and may include additional steps and/or maybe in a different order than those specifically described herein anddepicted in the Figures. For example, the extraction of mineralizedgelatin from bone may be dependent on a number of factors. In theprocesses of the present invention, acid or base concentration, ratio ofacid or base to bone, extraction temperature, extraction duration,sonication duration, and other variants can all affect the finalquantity and quality of the mineralized gelatin. Those skilled in theart reading this disclosure would be able to fine tune the presentmethods in accordance with the desired product, to arrive at a desiredquantity and quality of mineralized gelatin.

The methods of the present invention may further include performing oneor more additional extractions to form one or more additional extractedgelatin solutions, and optionally combining the one or more of theextracted gelatin solutions before the neutralizing step. The methodsmay further include reconstituting the freeze-dried mineralized carrierwith a liquid to form a liquid mineralized carrier. The methods mayfurther include cooling the liquid mineralized carrier to about roomtemperature or below to form a solid or semi-solid mineralized carrier.

FIG. 2 is a flow chart depicting non-limiting embodiments of methods offorming a mineralized carrier from bone in accordance with the presentinvention. According to the embodiments depicted in FIG. 2, corticalbone is exposed to acid, heat, and/or sonication to extract a gelatinsolution from the bone, which may then be further processed to form amineralized carrier. In the embodiments depicted in FIG. 2, according toa step (104) in the extracting process, cortical bone (102) is placed inan acid solution. The acid solution may include, but is not limited to,one or more acids such as hydrochloric acid, sulfuric acid, citric acid,acetic acid, and nitric acid. According to certain embodiments, such asthat depicted in FIG. 2, hydrochloric acid is used. The concentration ofthe acid solution may range from about 0.5 M to about 10 M. According tocertain embodiments, the concentration is about 1.0 M to about 3.0 M.The ratio of the bone to the acid may also affect the resulting gelatinquality. This may range from about 1 g in 1 ml of acid to about 1 g in20 ml of acid. According to certain embodiments, the range is about1:2.5 g/ml to about 1:5 g/ml.

In these embodiments, after the bone is placed in the acid solution, oracid is added to the bone, the bone is heated to dissolve the bonemineral and accelerate the breakdown of the collagen components of thebone into gelatin. According to certain embodiments, the acid may beheated prior to the bone addition. The heating may range from about 40°C. to about 100° C. to thermally degrade the collagen. According tocertain embodiments, the range may be about 60° C. to about 85° C.

A sonication step (106) may be used to ultrasonically agitate theparticles to accelerate the breakdown of collagen in the gelatinextraction process. Sonication of the bone, particularly while in acidat elevated temperatures can mechanically agitate the collagen intosmaller fragments. Mechanical agitation such as stirring,homogenization, grinding, or milling can also be used to physicallybreak apart the bone. In the example depicted in FIG. 2, sonication maybe used constantly through the extraction process or at specificintervals. Additionally, the extraction time can also be modified toimprove the effectiveness of the extraction step. For example, theextraction time can range from as short as 30 minute extraction cyclesto 24 hour extraction cycles. According to certain embodiments, anapproximately 2 to 4 hour extraction cycle is used.

After a set period of time, a separation step (108) is performed inwhich a first extract or extraction solution (116) may be removed. Theseparation is performed for example, by decanting, filtering, orcentrifugation extraction techniques. As long as the wet residual isseparated from the solution, it does matter which technique is used. Theresidual remaining after removal of the first extract may then befurther processed by steps that include the addition (110) of fresh acidto the residual), a sonication step (112) and a separation step (114) toremove a second extract or extraction solution (118) from the processedresidual. Further extraction steps (120) may be performed to anyremaining residual as desired or until the bone is essentially fullysolubilized.

After the extraction process is complete, the extraction solutions (116and 118) can be combined (122) into a single solution. A neutralizationstep (124) may then be performed using techniques such as, but notlimited to, buffering, dialysis, and ultrafiltration to form a gelatinsolution. According to certain embodiments, calcium hydroxide base maybe used in the neutralization. According to other embodiments, dialysistubes with a molecular weight cutoff of 10,000-15,000 Da may be used.Alternatively, each extraction solution may be separately neutralizedsoon after extraction. The extracts may optionally be frozen(independently or combined) before neutralization to prevent furtherbreakdown of gelatin fragments.

Depending on the concentration of the resultant neutralized gelatinsolution, the carrier may gel when cooled to a temperature of betweenabout 32 and 50° F., or about 2 to 10° C. FIG. 3 shows that the gelatinobtained by the present methods is visibly different than normal DBMderived gelatin. As depicted in FIG. 3, there is a clear distinctionbetween mineralized gelatin and normal gelatin. A standardized orspecific gelatin concentration may be obtained by performing afreeze-drying step (126) to freeze-dry the mineralized gelatin solutionto essentially isolate the mineralized gel. Once the mineralized gel isfreeze-dried, a reconstituting (rehydrating) step (128) may be performedin which the dry mineralized gel can be reconstituted (rehydrated) withwater or other solvent in a specific concentration to create astandardized gelatin solution. The standardized solution may then becooled in a refrigeration step (130) to form a gel. The concentration ofthe gelatin in water can be used to modify the properties of theresulting gels. Higher gelatin concentrations can be used for example,to create stronger gels. According to certain embodiments, a gelatinconcentration of about 2-10% g/ml can be used to create a gel carrierfor DBM particles. The gel may then be further processed (132) to formvarious mineralized carriers, such as DBM carriers.

The mineralized gelatin carrier may be stored, sold, or used in avariety of forms, including, but not limited to an unconstitutedfreeze-dried form resulting for example after step 126, in areconstituted liquid form resulting for example after 128, in arefrigerated gel form resulting for example after step 18, or as amineralized gelatin DBM carrier resulting for example after step 22.

The mineralized gelatin carrier may be used to fabricate a variety ofDBM products. For example, a DBM putty can be created by mixing dry DBMparticles into the mineralized gel. According to certain embodiments,the DBM concentration in the gel may be about 30-35% by weight. A puttycapable of being extruded through a syringe (often called a DBM gel orpaste) can be created by lowering the DBM content and increasing thegelatin content. According to certain embodiments, extrudable DBMputties can be formed using about 25-30% DBM concentration by weight.

DBM sheets and blocks can also be formed from the mineralizedgelatin/DBM mixture. In this form, a DBM product, such as DBM putty orgel, may be molded into a desired shape and then freeze-dried to removethe water component. The result is a DBM sponge capable of absorbingadditional fluid. These sponges are designed to be rehydrated forexample, by a surgeon inserting the bone product, with a liquidincluding, but not limited to, sterile water, sterile saline, blood,platelet rich plasma, growth factor solutions, marrow aspirate, and/orcellular suspensions (mesenchymal stem cells, osteoblasts, etc).

The present invention further provides mineralized carriers in variousforms including in a freeze-dried powder form, a reconstituted liquidform, and mineralized carriers capable of being formed into or actuallyformed into a solid or semi-solid mineralized carrier, such as putties,gels, blocks, sheets, sponges, or any other form contemplated by thoseskilled in the art. Accordingly, methods of the present invention mayfurther include one or more steps to achieve the desired form and/orshape. For example, the methods may include the step of forming theliquid mineralized carrier into a solid or semi-solid mineralizedcarrier selected from the group consisting of a sheet, putty, paste,block, and gel, and may optionally further include shaping the liquidmineralized carrier to form a shaped solid or semi-solid mineralizedcarrier.

Mineralized carriers in accordance with the present invention may becarriers formed by the present methods or may be formed by modifiedmethods, including other methods, which like the present methods,include the mineralized carrier being made directly from bone ratherthan from DBM, and/or result in mineralized carrier that include calciumand phosphate ions, such as calcium and phosphate salts. Accordingly,the present invention also provides mineralized carriers that includegelatin and calcium and phosphate.

Mineralized carriers in accordance with the present invention mayinclude the component being carried, such as DBM, and/or one or moreadditional components such as other biologically active ingredients,and/or thickening materials. Accordingly, the present invention furtherprovides bone products that include DBM and a mineralized carrier, suchas the carriers produced by the methods disclosed herein. The DBM andthe mineralized carrier may be integrally mixed in the bone product orin discrete portions of the bone product depending for example on theintended use of the product.

The one or more additional components that may be added to themineralized carriers or bone products of the present invention mayinclude any components that may be advantageous to bone grafting, aswould be apparent to those skilled in the art. For example, it may beadvantageous to add one or more biologically active ingredients to themineralized carrier of the present invention, which may or may not berelated to the connective tissue repair capabilities of the composition.Suitable active ingredients include DBM and the insoluble extractionproduct containing residual, bone morphogenetic proteins and relatedproteins such as cartilage derived morphogenetic proteins (CDMPs). Otheractive ingredients that may be added to the composition, includingbone-derived materials such as cortical or cancellous bone chips andbone mineral, osteogenic chemicals (e.g., L-arginine), osteogenicpeptides (e.g., OSA), osteogenic growth factors (e.g., transforminggrowth factor-beta [TGF-β], insulin-like growth factor [IGF], plateletderived growth factor [PDGF], vascular endothelial growth factor [VEGF],fibroblast growth factor [FGF]), and recombinant BMPs (e.g., rBMP-2,rBMP-7), fibronectin, and blood-derived proteins. When added inappropriate combinations, these active ingredients may assist bonerepair, cartilage repair, ligament and tendon repair, meniscal repair,and other musculoskeletal applications.

The product to be delivered, such as DBM, may be added to themineralized carrier at any of several steps in the process of making themineralized carrier, depending on the result to be achieved. Forexample, if it is desired that the DBM be integrally mixed with themineralized carrier in a final product, the DBM may be added to themineralized carrier in its freeze-dried or liquid form, before thecarrier is made into its final form and shape. The DBM may alternativelybe added to the mineralized carrier in its solid or semi-solid form, forexample where it is desired that the DBM and mineralized carrier mayform discrete portions of the final product, such as discrete portionsof a block. In addition, the mineralized gelatin may be used as acarrier for non-DBM containing bone graft materials. The gelatin may beused as a carrier for materials such as autograft, allograft corticalchips, allograft cancellous chips, synthetic bone graft particles,growth factors (such as BMP, TGF-B, VEGF, FGF), and/or cells (marrowcells, stem cells, bone cells, cartilage cells).

As indicated above, DBM products in accordance with the presentinvention, including for example, putty and gel, can be optionally mixedwith other graft materials such as bone chips (including for examplecortical and cancellous bone chips), synthetic graft granules, andautograft tissue. Other components may be added for example, to assistwith making the form of the carrier or bone product, such as componentsthat affect the viscosity, hardness, shape and other physicalcharacteristics of the carrier or bone product. For example, one or morethickening agents may be added to the carrier or DBM bone products ofthe present invention. Components may be added at various stages of theprocess of making the mineralized carrier or bone products, or afterformation of a bone product, such as to the surface of the bone product.

The one or more thickening materials in accordance with the presentinvention may be an active ingredient or biologically inert. Suitablethickening materials include for example, collagen, bone mineral, aninsoluble extraction product from the present methods, hydroxyapatite,tricalcium phosphate, biphasic calcium phosphate, calcium sulfate,calcium carbonate, biological glasses, and natural or syntheticpolymers. DBM, and/or a reverse phase medium may be used as a thickeningmaterial with or without added proteins. The reverse phase medium may bean aqueous mixture of Pluronic F127 (BASF Corp.) in an amount sufficientto confer a reverse phase property to the composition, such asapproximately 20-40% w/w, or about 23-32% w/w, or about 25% w/w or about35% w/w mixture of Pluronic® F127 and water. Other reverse phase mediainclude aqueous mixtures of derivatives of Pluronic® F127.

The biological, physicochemical and biodegradation properties of thecomposition may be altered by known cross-linking agents such aschemicals (e.g., glutaraldehyde or formaldehyde) or radiation (e.g.gamma or electron beam). For example, electron beam (E-beam) radiationmay be used to irradiate the wet or dry materials at doses between about5 and about 50 kGray.

Resulting products or compositions of the present invention may be usedin several different manners. DBM products in accordance with thepresent invention can be prepared for, for example, injection orinsertion at, into, onto, or near bone or chondral defect sites,cartilage repair sites, or other musculoskeletal sites. The manner ofinjection or insertion is not essential, but may be for example viasyringe in the case of injection and insertion may be by creating asurgical opening to access the bone or chondral defect site.

According to certain embodiments, a composition including the carriersor products of the present invention may be applied to lyophilized,cancellous bone chips; or bone chips may be dipped into the composition.The bone chips, coated with the composition, may be dried. The dryingstep may be conducted by any conventional drying process, includinglyophilization or oven drying. The coated bone chips may be used as orin surgical implants at, in, on, or near bone defect sites, cartilagerepair sites, or other musculoskeletal sites. Alternatively, the coatingmay be applied to larger segments of bone, artificial implants, or anyother kind of surgical implant.

Alternatively, the dry soluble extraction product or concentrate may bemixed with aqueous alcohol or other volatile solutions, cast into adesired shape and dried to form a sponge-like material. For example, oneto six carbon alcohol, such as ethanol, may be used. Moreover, 1 to 20percent alcohol by volume solution may be used. The resultingcomposition may be cast into a sheet or other shape with or withoutother added materials. The sheet or other shape is dried. Drying may bedone by any conventional method, including lyophilization or air-drying.Preferably, drying is by lyophilization.

In certain embodiments, the sheet or shape formed with an alcoholsolution as described above may be used as or as part of a surgicalimplant. Where a sheet is used, it may be used as a wrap around an areaor as a patch inserted into a bone defect site, e.g., insertion into abone defect, a chondral defect, a spinal fusion cage or a pre-reamedacetabular bed.

Products in accordance with the present invention can also be used as acoating on surgical implants or devices to be inserted at, into, onto ornear bone defect sites, cartilage repair sites, or other musculoskeletalsites. Accordingly, the present invention further encompasses surgicalimplants or devices comprising a surgical implant coated with amineralized carrier and/or a bone product or composition, which includesa mineralized carrier in accordance with the present invention.

The present invention is further directed to kits that include amineralized carrier in accordance with the present invention. Themineralized carrier may be in powder, liquid, solid or semi-solid form,for example in the form of a gel, putty, paste, sheet, block, sponge orother form. Accordingly, the mineralized carrier may be included in thekit independent from the item to be carried, or may be in the kit in afinal, bone product form, or as a coating or component of a surgicalimplant or device included in the kit. In kits where the mineralizedcarrier is included independently from the component to be carried, thekit may further include the component to be carried (such as DBM). Suchkits including the carrier and component to be carried separately wouldallow a user to determine which ratio of e.g., DBM to carrier they wishto use.

Kits in accordance with the present invention may include one or more ofthe following: a liquid for reconstituting mineralized carrier from apowder form; a liquid to be added to a bone product in a sponge form; acontainer for combining the carrier with one or more other components;and/or an apparatus (such as a form or mold) in which or on which toform a carrier into a specific shape. Kits may further include any othercomponents to be combined with or added to the carrier. Furthermore,kits in accordance with the present invention may include one or moretools or other components to assist in inserting a bone product,surgical implant or device into a patient.

The present invention further includes methods of treating a patient,which include providing a patient in need of treatment, such as apatient with a bone defect, with a bone product and/or an implant thatincludes a bone product (for example coated on the implant), inaccordance with the present invention.

The following examples illustrate specific embodiments of the invention.The examples set forth herein are meant to be illustrative and shouldnot in any way serve to limit the scope of the claimed invention. Aswould be apparent to skilled artisans, various changes and modificationsare possible and are contemplated within the scope of the inventiondescribed, and may be made by persons skilled in the art withoutdeparture from the spirit of the invention.

EXAMPLES Example 1

This example details an extraction process according to certain methodsof forming a mineralized carrier in accordance with the presentinvention. Cortical bone is heated in an oven at about 85° C. for about1 hour, and sonicated at about 60° C. for about 1 hour. This is repeatedonce for a total extraction time of about 4 hours. At this point, theextraction solution is isolated from the residual bone throughtechniques such as decanting, or filtration, resulting in a firstextract. This first extract can be frozen to prevent further breakdownof the gelatin fragments or can be immediately neutralized usingbuffering, dialysis, ultrafiltration, or other neutralizationtechniques.

The residual bone is then put through additional extraction steps withfresh acid until the collagen is completely dissolved. The subsequentextraction steps may be conducted using modified extraction conditionsto fully dissolve the remaining collagen. The second extraction includedexposing the residual bone to fresh 1 N HCl in an oven for about 1 hourfollowed by sonication at about 60° C. for about 1 hour, resulting in asecond extract. The second extract can be frozen to prevent furtherbreakdown of the gelatin fragments, can be combined with the firstextract before neutralization, or can be immediately neutralized usingbuffering, dialysis, ultrafiltration, or other neutralizationtechniques. The extract can then be freeze dried to allow for futurereconstitution.

Example 2

The freeze dried mineralized gelatin from Example 1 can then be combinedwith sterile water to produce a 5% gelatin solution. Once fullydissolved, the gelatin solution is placed in a refrigerator at 4° C. tocause the material to gel. At this point, a mixture of 30% DBM and 70%gelatin (by weight) can be formed to create a moldable DBM putty. Oncethoroughly mixed, the DBM putty is stable at room temperature.

Although this invention has been described in certain specificembodiments, many additional modifications and variations would beapparent to those skilled in the art. For example, many modificationsmay be made by those skilled in the art to the process conditions, suchas temperature, amount and type of acid, base and, or salt used, amountof sonication, number of extraction repetitions, and the like to achievea desired product. It is therefore to be understood that this inventionmay be practiced other than as specifically described. Thus, the presentembodiments of the invention should be considered in all respects asillustrative and not restrictive.

1. A method comprising solubilizing and extracting gelatin solution frombone, while retaining minerals from said bone in said gelatin solution;neutralizing the pH of the extracted gelatin solution to form aneutralized mineralized solution; processing the neutralized mineralizedsolution into a mineralized carrier comprising bone gelatin andsolubilized minerals from bone; and adding one or more bone graftmaterials to the mineralized carrier to form a bone product for surgicalimplant.
 2. The method of claim 1, further comprising freeze-drying theneutralized gelatin solution to form a freeze-dried mineralized carrier.3. The method of claim 1, further comprising performing one or moreadditional solubilization and extraction steps to form one or moreadditional extracted gelatin solutions.
 4. The method of claim 1,wherein the extraction includes agitation of the bone.
 5. The method ofclaim 1, wherein the extraction includes treating the bone with acid. 6.The method of claim 1, wherein the extraction includes heating the boneat a temperature between about 40° C. and about 100° C.
 7. The method ofclaim 2, further comprising reconstituting the freeze-dried mineralizedcarrier with a liquid at room temperature or above to form a liquidmineralized carrier.
 8. The method of claim 7, further comprisingcooling the liquid mineralized carrier to below room temperature to forma solid or semi-solid mineralized gel carrier.
 9. The method of claim 2,further comprising adding demineralized bone matrix to the mineralizedcarrier after freeze drying.
 10. The method of claim 7, furthercomprising adding demineralized bone matrix to the liquid mineralizedcarrier.
 11. The method of claim 8, further comprising addingdemineralized bone matrix to the solid or semi-solid mineralizedcarrier.
 12. The method of claim 1, further comprising adding one ormore additional components selected from the group consisting ofcortical bone chips, cancellous bone chips, synthetic graft granules andautograft tissue, after said solubilizing and neutralizing steps. 13.The method of claim 1, wherein the bone is selected from at least one ofcortical bone or cancellous bone.